(Adapted from Applicant's Abstract) There is no means of coronary heart disease prevention for men that combines the qualities of safety, effectiveness, wide acceptability and low cost. While the "statin" group of compounds, e.g., lovastatin, pravastatin, is effective in preventing coronary events, there are issues regarding side effects, compliance and cost that limit their use. Soy phytoestrogens may represent an alternative to pharmacologic means of coronary heart disease prevention. There is limited evidence indicating that soy consumption inhibits atherogenesis and has favorable effects on coronary vascular reactivity while having favorable or neutral effects on other organ systems. The major objective of Project 2 is to assess the usefulness of soy phytoestrogens in primary cardioprotection of adult male monkeys. The study will address directly whether long-term soy consumption is without adverse effects on the reproductive system, cognition, social or sexual behavior and function and determine if it has favorable effects on the prostate gland. Ninety cynomolgus monkeys will be randomized to three treatment groups: 1) placebo atherogenic diet (n=30), 2) low phytoestrogen atherogenic diet (58 mg/1800 Cal) (n=30) and 3) high phytoestrogen atherogenic diet (120 mg/1800 Cal) (n=30). Diets are identical in atherogenicity and nutritional content; they differ only in phytoestrogen content. During a 36 month treatment period, assessments will be made of plasma lipoproteins, blood pressure, arterial vasomotor function, sociosexual function, testicular endocrine and spermatogenic function, and cognitive function. Postmortem assessments will be made of atherosclerosis extent and arterial expression of estrogen receptors (alpha and beta). In addition, immunohistochemical and histomorphometric markers of prostatic hyperplasia and neoplasia will be studied as will histomorphometric markers of mammary gland hyperplasia and neoplasia. Spermatogenesis will also be assessed. Finally, assessments will be made of behavior-relevant immunohistochemical markers of estrogenic stimulation in the central nervous system. Since the body of data that exists currently regarding the effects of soy on the cardiovascular, reproductive, and central nervous systems is quite limited, this study represents a necessary step in elucidating the potential for a favorable public health impact of widespread soy consumption by men.